There are many reports on researches made with a view to increasing the sensitivity of a shaped material, for example, a fiber, and various techniques are disclosed. It is well known that the development of, in particular, a chromatic fiber capable of changing its color depending upon the external environment is in an advanced stage. A typical example thereof is a fiber which responds to temperature, light, etc.
Used therein is a technique of combining a fiber with a material inherently having a chromatic function (e.g. a thermochromic acrylic fiber obtained from a polymer mixed with a thermochromic granular material, disclosed in Japanese Patent Application Kokai Laid-Open) No. 62-184114), and there are very few examples of a technique of imparting a color-changing function to a fiber per se.
As the example of, in particular, a technique of endowing a fiber with a function of changing its color depending upon its moist or dry condition, there can be mentioned at best a method of mixing a fiber with cobalt ion. This method has problems in that the color-changing function is markedly reduced owing to the falling-off of the material having said function and further the speed of color change response is low.